Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.

Because its surface is very far away from where the fusion reactions are occurring. The size of the core fusion region does not scale with the radius of the star, especially for giant stars. Or another way to think about it, there's some rate of energy output by fusion reactions, but you're spreading that out over a very large area, so the energy output per unit area is less.